Serial Attached SCSI (SAS) is a computer bus used to move data to and from devices such as hard drives and tape drives. A typical SAS system may include one or more initiators and one or more target devices. Certain SAS systems with large numbers of devices may utilize SAS expanders to facilitate communications between the initiators and various target devices.
A typical SAS expander may include two or more ports for establishing communications between two or more devices (e.g., between an initiator and a target). A routing table (e.g., implemented utilizing a Content-Addressable Memory, or CAM) may be used to keep information about which SAS address can be accessed via which port of the expander. For example, when an OPEN address frame (OAF) is received on one port of the expander, the expander may perform a routing table lookup to find on which phy the OPEN address frame should be routed to. The routing table may have one entry per SAS address, which means that the number of table entries needed for a given topology may increase linearly with respect to the size of the topology. Increasing the routing table size may slow down its lookup speed.
Furthermore, conventional expander systems may utilize one central routing table. As the number of ports increases, the numbers of simultaneous routing table lookup requests may increase drastically. Since these requests need to be prioritized and processed one at a time, the overall connection latencies for requesting resources may be increased as a result. Therefore, the conventional expanders based solely on central routing tables are not scalable to support port number increases without affecting connection latencies.